4L60E/241C info

[A1971Blazer]

This drivetrain will be going in a '71 K5........
'02 LS1 4L60E


I'm gonna ditch the 205 transfer case and go with the 241C
Now, my question is, the 4L60E is 2 wheel drive.......I know the tailshaft housing can be changed to a TC adapter but what about the output shaft on the transmission? Will it need to be changed to work as a 4x4?
From what I can find, the TC is a 27 spline input but, does it use a coupling sleeve or is it female.......?
Forgive my ignorance.....I just don't know much about that transmission/TC combination.

[BR3W CITY]

The output shafts in the and entire tail housing are longer for the 2wd models. As far as I know (I'm not a 4x4 guy, but I pick up stuff along the way), you can start with a 2wd 4l60e if your going to the 241 tc, since you need to change the output shaft either way.

If you stuck with the 205, the starting with a 4wd 4l60e would be easier because you could just bolt it up.

edit; so I guess the 241 was either 21 or 23 spline depending on the year and application. Thats why the output shaft needs to get changed to accomodate the difference in spline count.

Take a look at this little info section and adapters I found through a jeep site.
http://www.novak-adapt.com/catalog/a...e/kit_4l61.htm

[First c10]

Might be easier to get a 4x4 4L60E Trans and bolt the 241 directly together. This is what I am doing.
The novak part is expensive and you still have to do the work or pay to have it done. Nice option though.
Let us know what you do and take a lot of pictures

[BR3W CITY]

But don't the 4x4 4l60e and the 241 have different spline counts? The way I took it, you'd have to change the output shaft either way since the spline count would be wrong.

[First c10]

well I am not sure...I have a 2008 4L60 with a 1990 NP241C and they bolt right up. I do remember something about the older 4L60 having a different spline count (I think)!!!!
Brew could that be it?

[A1971Blazer]

From what I have found so far.......the 241 that fits the 4L60E has a 27 spline input....I talked to a TC builder that advertises on Ebay...he says he can build one with either a 27 or 32 spline. I think the 32 spline went on a 4L80E..?

[First c10]

The 32 spline is the TC400/4l80 and 6l80. I am not sure about the actual spline count on the 4L60

[A1971Blazer]

It's turning out that, so far, the 241 passenger drop is as rare as dinosaurs.....
I'm researching using a 208 since this will be a driver and the 208s are more plentiful.......any experience with 208s anybody...........?

I had an '83 Jimmy that I'm pretty sure must have had one......seems like it didn't shift real well........?

Here's a shot when the divorce became final.......................

[First c10]

I used a 1991 Suburban NP241C its even has the VSS sensor for the computer. They used a 4L60E also

[A1971Blazer]

Originally Posted by First c10

I used a 1991 Suburban NP241C its even has the VSS sensor for the computer. They used a 4L60E also

That's what I'm not having any luck finding.................there has to be a good used one somewhere...?

[First c10]

I know of a 1990 here that has one but not sure what it would cost to send to you or the cost of the case I paid 300$ for mine and rebuilt it to be sure.

[First c10]

I meant I spent $200 for the t-case and a 100$ for parts to rebuild it.

[A1971Blazer]

Found a 1990 Suburban with the NP241C right hand drop!
$325.00 shipped from South Dakota........

First C10........what did you do for the shifter bracket?

[First c10]

I got the shifter bracket and linkage with the TC from the junk yard all from the same vehicle.

[A1971Blazer]

Originally Posted by First c10

I got the shifter bracket and linkage with the TC from the junk yard all from the same vehicle.

I asked the seller for those as well........it might make it much easier. Probably need to get the transmission adapter as well.
Would the '90 Burb have the 4L60E?

[First c10]

It might not be a 4L60E it might be just a 4L60 (no E) either way it should work or a 700R4 which I think is the same also. I would ask for the adapter at the same time. I would even ask for the Cross member as they are different then the 67-72 cross members. When I get to my shop I will post a picture of all I got for my sons truck.

[First c10]

This is the crossmember for the transmission and TC I got when I bought the TC out if the 91 burb. Also got the TC skid plate.

[A1971Blazer]

Kind of a crap shoot on the tranny adapter.....? I'm gonna contact the seller today to see if he will look at the adapter when he pulls the TC.
I do know that the 700R4 has a 4 bolt mount flange whereas the 4L60 has a 6 bolt ("hex) pattern.


This is the rear of the 4L60E main case.
I have it disassembled for rebuild and upgrades.
Also did some measuring and drew it up in CAD case I need to machine my own adapter.
Attachment 1378261

[First c10]

A1971blazer,
When I click on your link I get
"Invalid Attachment specified. If you followed a valid link, please notify the administrator"

I will take a picture of my adapter when I get to the shop this evening for you. It would be nice to know if the '90 burb had a 4L60 from factory.....
The attached picture was from my sons C10 build. It was a 6L80E 4x4 trans I converted to 2wd. I think it was mated to a NP263 I think. The motor/trans is out of a 2011 1500 4x4 Truck.

[A1971Blazer]

Thanks....!
I'm not sure about the picture...I put the wrong one, deleted it, then put in the correct one......who knows......?
I asked the seller to throw in the adapter....hopefully he will.....just in case it's the correct one.
Another try.......back of 4L60E tranny case

[clinebarger]

A '90 1/2 ton Suburban will have a 700R4 & a 4-bolt adaptor, Though technically it is a 4L60, But causes confusion to call them that.

'93-'97 4L60E's also have 4-bolt cases.

The 6-bolt Modular 4L60E came out in '98 (Full production), Some '96 & '97 C/K trucks did have them.

[A1971Blazer]

Originally Posted by clinebarger

A '90 1/2 ton Suburban will have a 700R4 & a 4-bolt adaptor, Though technically it is a 4L60, But causes confusion to call them that.

'93-'97 4L60E's also have 4-bolt cases.

The 6-bolt Modular 4L60E came out in '98 (Full production), Some '96 & '97 C/K trucks did have them.

Thanks for that info...!

So that means the adapter will have to be from a 98 up 4L60, or a short 4 bolt to 6 bolt adapter plate, or use an earlier 4L60E tranny case?
Also I understand that the 241 may have 5 hole or 6 hole mount....correct?

I suppose I'll just wait for the TC to get here then figure out the mounting.

I started with the transmission side creating a 3D model for an adapter that I could machine myself from billet aluminum.

It will be a bit more time consuming but I'm also thinking that I will be able to clock the TC precisely and put the cross member mount surface exactly where it needs to be.

Beginning of the adapter solid model.
Mounting surface on transmission side......6061-T6 billet aluminum

[clinebarger]

Originally Posted by A1971Blazer

Thanks for that info...!

So that means the adapter will have to be from a 98 up 4L60, or a short 4 bolt to 6 bolt adapter plate, or use an earlier 4L60E tranny case?
Also I understand that the 241 may have 5 hole or 6 hole mount....correct?

I suppose I'll just wait for the TC to get here then figure out the mounting.

I started with the transmission side creating a 3D model for an adapter that I could machine myself from billet aluminum.

It will be a bit more time consuming but I'm also thinking that I will be able to clock the TC precisely and put the cross member mount surface exactly where it needs to be.


Beginning of the adapter solid model.
Mounting surface on transmission side......6061-T6 billet aluminum
Attachment 1378775

I'm a automatic trans guy, My 4x4/Transfer case knowledge is limited, In North Texas we pave everything.

First off, Use the "300mm" Modular 4L60E you have now, For a few reasons

300MM 4L60E's are designed for use behind LS engines, You could adapt a 4-bolt "298mm" 4L60E to fit, But it's not worth it, Especially with a transfer case hanging off the back, The T-case will pull the bolt threads right out of the trans case if all the correct braces are not used. The braces are hard to find because dumb$hits throw them away because they don't want to go through the hassle of reinstalling them.

The 6-bolt modular case has a lot more torsional rigidity than a 4-bolt case, And 6-bolts holding the T-case eliminating the need for braces.

T-case adaptor for a 6-bolt 4L60E to a NP241 Driver side drop...part#
15005474, There is one on E-Bay for $50 HERE

I do now know if this will work on a Passenger side drop NP241, I have not done this myself...So do your research!

Machining your own adaptor would be cool, But Modular case 4L60E's do not have trans mount provisions on the case itself, The Mount pad has to be on the adaptor for 4x4's & the Extension housing on 2wd's.

Not sure on the 5-bolt vs 6-bolt on the T-case side, All 4x4 fullsize trucks I have dealt with have 6 bolts, Like I stated above "limited knowledge".

If you need help swaping the output shafts on the trans, I can help with that.

**Don't be alarmed about the 6-bolt adaptor being longer than a 4-bolt adaptor, When GM redesigned the case, They eliminated the "length" the Governor took up on 700R4 style cases & added the length to the adaptor/extension housing, Also the reason the mount pad got eliminated**

[A1971Blazer]

Excellent information there.............thanks again!
The TC will be here this week, then I can start to work it all out. I have the 4L60 bare case and the bellhousing so I will be able to start mounting the engine and drive line once I get an adapter....

I only got as far as creating the geometry to match the transmission on a billet adapter...........that's the only piece I have.....the cross member mount would be designed and milled as an intregal part of it once I get the transfer case dimensions.....getting a factory mount will be much easier and faster.

[First c10]

This is the mating surface of the TC 241c.